I installed the top flight dummy radial. the radial is a bit larger than the cowl. I had to use the dremel to grind the radial down quite a bit to get it to fit. Had to take the tops off a few cylinders to get it to fitt right with my OS91. Noethless, you cant see it and it looks really really nice. I even wittled a wooden chin to put in the cowl. Definitley recommend the radial and homemade chin.